SL6's gdm does not honor the exit code from /etc/gdm/PreSession/Default. In SL5x, it used to abort the login if the script returns a non-zero exit code. I used this feature to put up a zenity dialog which the user had to click yes in order to continue logging in. Now, the user logs regardless of the script.
In fact, the distro's Default script is empty. It used to contain the xsetroot and sessreg bits.
Any workarounds?